The real concerns involve sustainable agricultural concerns such as pesticide resistance or overuse, gene contamination, and freedom of research, and specifically if Monsanto the company has really shown themselves to be the most responsible steward to retain near-monopolistic control over the execution of these sensitive practices, as well as a vast proportion of the world's seed supply.
For lots of in-depth discussion on these issues, I recommend this series by the Union of Concerned Scientists: http://www.ucsusa.org/food_and_agriculture/our-failing-food-... Articles specific to Monsanto are here: http://www.ucsusa.org/food_and_agriculture/our-failing-food-... http://www.ucsusa.org/food_and_agriculture/our-failing-food-... http://www.ucsusa.org/food_and_agriculture/our-failing-food-...
Disclaimer: I am not a farmer, or a scientist, or someone who knows anything at all. I am merely pointing out that this article says nearly nothing useful, and referring to a series of articles by a reputable, if not opinionated, organization of experienced scientists and researchers.